If you doubt or disregard those experiments on the basis of them being dream-like, or if you reinterpret them as something which in reality says something totally different from what it actually says (i.e. that it's all just some cryptic symbolic message), the same applies to anything and all, potential symbols included.

Following your standard, symbols would by definition communicate what they don't actually communicate. Thus, you would get an infinite regression of symbols communicating symbols communicating symbols, etc., but no actual message.

Why would you, then, even consider what any symbol might possibly communicate to the dreamer? In your scenario, it would be impossible to tell, and the only valid answer (to all questions) would be, "I don't know absolutely anything," which is clearly neither the case nor true.